The present invention relates generally to a power line communication system for transmitting a ballast dimming level to an electronic ballast.
More particularly, this invention pertains to a power line communication system that has improved noise immunity for transmitting the ballast dimming level to the electronic ballast.
Electronic ballasts are utilized to generate and control the amount of power consumed by gas discharge lamps. The ballast dimming level determines the power output of the electronic ballast and therefore the lighting intensity of the lamp. A ballast dimming level may be communicated to a power line receiver associated with the electronic ballast. The power line receiver receives a ballast control signal having dimming level information and generates a dimming level signal corresponding to the desired ballast dimming level. The dimming level signal then causes the electronic ballast to generate an AC lamp signal to the lamp in accordance with the desired dimming level. In this manner, a user can control the power consumed by the lamp.
Often, it is advantageous to communicate the lamp dimming level over the AC power signal that powers the electronic ballast. A power line controller may be utilized to insert information on the AC power signal to communicate the desired dimming level to the power line receiver. The power line controller generates the ballast control signal and inserts that ballast control signal on the AC power signal. The power line receiver then extracts this information from the AC power signal to generate the appropriate dimming level signal. Typically, the dimming level signal is transmitted to an inverter control circuit which controls the amount of power generated by the ballast to the lamp.
Several prior art solutions exist for transmitting information to the electronic ballast over AC power lines, including using power line modems, high frequency injection codes and line voltage modulation codes. Unfortunately, the equipment required to insert information into the AC power signal and then extract the information at the ballast is expensive. Furthermore, these systems are particularly sensitive to noise and require ballast control signals with high signal levels to communicate the desired ballast dimming level over the power line. This is particularly true if the system is communicating with several electronic ballasts at once.
What is needed, then, is a power line communication system that inserts information on the AC power signal that is more cost efficient and less sensitive to noise.